1. Field of the Invention
The present invention relates to a mobile communication technology, and more particularly to a mobile communication technology that uses the Orthogonal Frequency Division Multiplexing (OFDM) for the transmission method in a wireless section.
2. Description of Related Art
The widespread use of the Internet in the mobile communication field increases the need for high-speed web access and data communications including music and video. To meet this need, much effort is being made to study high-speed, broadband communications. One of the third-generation mobile communication systems is a 1×EV-DO (1× Evolution Data Optimized) system. The 1×EV-DO system uses the Code Division Multiple Access (CDMA) method for the transmission method in a wireless section. The 1×EV-DO Rev. A (Revision A) commercially available today provides the uplink communication speed of 1.8 Mbps and the downlink communication speed of 3.1 Mbps.
In addition, study is also being conducted on the application of the OFDM method, which is now used for a wireless LAN or digital broadcasting, to the mobile communication system. In the LTE (Long Term Evolution) system, one of the 3.9-generation mobile communication systems, the use of the OFDM method is already decided and the standardization work is being carried out. In addition, the fourth-generation mobile communication system IMT-Advanced (International Mobile Telecommunications-Advanced), which is the next generation communication system, also uses the OFDM method.
As compared with the CDMA method, the OFDM method uses the frequency more efficiently and ensures high-speed data transmission in a broadband system.
On the other hand, it is stipulated in the LTE standardization activity that the uplink data communication speed of 50 Mbps and the downlink data communication speed of 100 Mbps are possible in the 20 MHz bandwidth. The IMT-Advanced system is thought of as a system that will implement the downlink data communication speed of 1 Gbps in the 100 MHz bandwidth.
In the third-generation mobile communication system, the system is used primarily for the mail, web browsing service, and short-time video downloading. In the forthcoming 3.9-genration/4-generation mobile communication system, a larger amount of data communication is possible with focus on the long-time streaming services such as online movies and online games.
Unlike in the wired communication, a terminal is supposed to constantly move in the mobile communication. Because the quality of a wireless channel is subject to the landform of a place where the terminal is used, the interference waves such as reflective eaves from obstructions, and the other users who are in connection, the reception quality of the terminal may depends largely on the place where the terminal is used. Especially, when the user is receiving long-time streaming services such as online movies or online games described above, there is a possibility that, after a successful connection, the reception quality is too low to use the service, a drop in the reception quality during the service suddenly delays or even stops the data reception, or the communication is disconnected during the service, with the result that the user is highly dissatisfied. In this case, the ability for the user to know the serviceable communication quality before using the service, if available, wound allow the user to know the serviceable communication quality in advance and to judge whether to use the service. As a result, the user can use the service more reliably and feels satisfied.
When the required communication quality is not expected, it is expected that users will voluntarily refrain from using the communication services and, as a result, the base station will use the resources more efficiently. That is, if a user who has intended to view a movie from 10:00 PM gives up viewing it because of poor communication quality and releases the resources, other users will use the released resources and the general throughput of the base station will increase.
In today's mobile communication system, the reception level indicator and the out-of-area indicator are displayed as means for informing a mobile terminal user about the communication quality. However, the reception level indicator of a terminal only indicates the level of the waves received from the base station and, even when all antennas appear, it cannot be judged that the quality of data communication is good.
JP-A-2005-159486 and JP-A-2002-300644 disclose technologies for estimating not only the reception level of electric waves but also the data transmission speed of communication after a connection is established. JP-A-2002-300644 discloses a technology that estimates the data communication speed using the parameters specific to the 1×EVDO system and displays the data communication speed on a mobile terminal. Because the 1×EVDO system uses the CDMA method as the transmission method, this technology cannot be applied directly to the OFDM system.
In addition to the technologies described above, JP-A-2004-172907 discloses an invention in which a base station calculates an acceptable communication rate in response to a required communication rate notified by a mobile station.